Implement setNativeSelectedIndex command for Picker component
Implement setNativeSelectedIndex command for Picker component

Summary:
This is required so we can switch to using commands instead of `setNativeProps`.
`setNativeProps` are not supported in Fabric, we are moving away from it.

Reviewed By: JoshuaGross

Differential Revision: D17764967

fbshipit-source-id: 16e54ebe1f0c58b80a6491db970a60c01fec8a15

hammerandchisel/react-native,myntra/react-native,pandiaraj44/react-native,javache/react-native,javache/react-native,myntra/react-native,exponentjs/react-native,pandiaraj44/react-native,exponent/react-native,javache/react-native,javache/react-native,myntra/react-native,janicduplessis/react-native,hoangpham95/react-native,javache/react-native,arthuralee/react-native,janicduplessis/react-native,arthuralee/react-native,pandiaraj44/react-native,arthuralee/react-native,hammerandchisel/react-native,exponent/react-native,myntra/react-native,hoangpham95/react-native,exponentjs/react-native,janicduplessis/react-native,facebook/react-native,facebook/react-native,pandiaraj44/react-native,hoangpham95/react-native,facebook/react-native,exponent/react-native,exponentjs/react-native,janicduplessis/react-native,myntra/react-native,janicduplessis/react-native,facebook/react-native,exponent/react-native,myntra/react-native,pandiaraj44/react-native,myntra/react-native,hammerandchisel/react-native,hoangpham95/react-native,javache/react-native,myntra/react-native,exponentjs/react-native,hammerandchisel/react-native,exponent/react-native,javache/react-native,pandiaraj44/react-native,hoangpham95/react-native,facebook/react-native,facebook/react-native,javache/react-native,exponent/react-native,janicduplessis/react-native,facebook/react-native,facebook/react-native,hammerandchisel/react-native,hammerandchisel/react-native,myntra/react-native,exponent/react-native,hoangpham95/react-native,exponentjs/react-native,exponentjs/react-native,facebook/react-native,exponentjs/react-native,javache/react-native,pandiaraj44/react-native,hammerandchisel/react-native,arthuralee/react-native,janicduplessis/react-native,exponent/react-native,hammerandchisel/react-native,hoangpham95/react-native,janicduplessis/react-native,arthuralee/react-native,exponentjs/react-native,pandiaraj44/react-native,hoangpham95/react-native